CHICAGO (AP) -- A Chicago jury convicted Oscar-winner Jennifer Hudson's former brother-in-law on Friday of murdering her mother, brother and 7-year-old nephew in what prosecutors described as an act of vengeance by a jilted husband.

Hudson, who expressed her undisguised disdain for William Balfour when she took the witness stand and endured weeks of excruciating testimony about the 2008 killings, was overcome with emotion as the verdict was read. She bit her lip, tears welling in her eyes and streaming down her cheeks. She then looked at her sister, Julia Hudson, and smiled.

The sisters left the courthouse without speaking to reporters but released a statement Friday night extending a prayer to the Balfour family, saying "we have all suffered terrible loss in this tragedy."

"It is our prayer that the Lord will forgive Mr. Balfour of these heinous acts and bring his heart into repentance someday," they said in the statement, which also thanked prosecutors for their "dedication and tireless work" and praised police and trial witnesses.

Balfour, who faces a mandatory life prison sentence, showed no emotion after the verdict. A few of his relatives looked upset, one repeatedly shaking her head and muttering that the verdict was unfair.

Jurors deliberated for three days before reaching their verdict against Balfour, a 31-year-old former gang member who was the estranged husband of Julia Hudson at the time of the murders. Just an hour before their unanimous verdict on all counts, jurors sent a note to the judge that three jurors still weren't fully convinced of his guilt.

With no surviving witnesses to the Oct. 24, 2008, slayings or fingerprints, prosecutors built a circumstantial case against Balfour by calling 83 witnesses over 11 days of testimony. Witnesses said he threatened to kill the entire family if Julia Hudson spurned him.

Balfour's attorneys proposed an alternate theory: that someone else in the crime-ridden neighborhood on Chicago's South Side targeted the family because of alleged crack-cocaine dealing by Jennifer Hudson's brother, Jason Hudson. During the 30 minutes in which they called just two witnesses, however, they presented no evidence to support that theory.

Cook County State's Attorney Anita Alvarez, who spoke to Hudson after the verdict, said the star was visibly relieved. She said Hudson had been determined to attended every day of the trial out of a sense of obligation to her mother.

"She told me, `If it was me (who had been killed) my mother would be here every day. So, I'm going to be here every day,'" Alvarez said.

Public defender Amy Thompson said she would appeal the verdict.

"It has always been our position and it still is that William Balfour is innocent of these murders," Thompson said.

Alvarez reiterated to reporters what prosecutors had told jurors: that the evidence against Balfour was overwhelming.

Jurors told reporters afterward that their deliberations were thorough and cordial, and that Jennifer Hudson's celebrity didn't influence them. They said it took time to piece everything together, and that a key was cellphone records showing Balfour was in the area when the killings happened.

Jennifer Hudson, who was in Florida at the time, attended every day of the two weeks of testimony, sobbing when photos of her relatives' bloodied, bullet-ridden bodies were displayed to jurors during closing arguments.

Alvarez said Hudson would not speak to the media about the verdict but would release a statement "at the appropriate time."

The jury foreman said he hoped the verdict would bring Hudson closure.

"I hope she can put this thing behind her and get on with the rest of her life," Robert Smith, a 47-year-old employee at Chicago Public Schools told reporters outside court.

Hudson, 30, rose to prominence as a 2004 "American Idol" finalist. But she became a bona fide star for her performance in the film adaptation of the musical, "Dreamgirls," for which she won the 2007 Academy Award for Best Supporting Actress.

Hudson was the first witness prosecutors called to testify, and during her more than 30 minutes on the stand she talked about her murdered family members and spoke endearingly about her nephew, Julian King, whom she called Tugga Bear. She said she knew Balfour since the eighth grade and always deeply disliked him.

Balfour had lived in the Hudsons' three-story Englewood home after marrying Julia Hudson in 2006. He moved out in early 2008 after falling out with his wife, but witnesses told jurors he often stalked the home.

The killings occurred the morning after Julia Hudson's birthday, and prosecutors said he became enraged when he stopped by the home and saw a gift of balloons in the house from her new boyfriend.

After his estranged wife left for her job as a bus driver on the morning of Oct. 24, 2008, prosecutors said Balfour went back inside the home with a .45-caliber handgun and shot Hudson's mother, Darnell Donerson, 57, in the back; he allegedly then shot Jason Hudson, 29, twice in the head as he lay in bed.

Prosecutors said Balfour then drove off in Jason Hudson's SUV with Julian — Julia's son, whom she called Juice Box — and shot the boy several times in the head as he lay behind a front seat. His body was found in the abandoned vehicle miles away after a three-day search.

The defense tried to counter the portrayal of Balfour as an embittered husband by noting Julia Hudson continued to have sex with him until just days before the killings.

In heated closings Wednesday, Thompson, almost shouting, said prosecutors had failed to prove their case. Prosecutor James McKay shot back that the defense was exploiting a popular misunderstanding that circumstantial evidence is lesser evidence.